1a. Objectives (from AD-416):
To identify membranes that can reduce the microbial activity and antibiotic residues in the liquid processing streams from fuel ethanol processing facilities; Study the heat transfer fouling characteristics of the processing streams after membrane treatment; Evaluate the processing and economic effects of membrane incorporation by modification of ERRC’s ethanol processing model.
1b. Approach (from AD-416):
Several types of membranes will be used to filter process streams such as thin stillage obtained from commercial fuel ethanol production facilities. Permeate and retentate streams from the filtrations will be characterized for microbial activity and antibiotic residuals. This will be done using a non-hazardous challenge organism and commercially used antibiotics. Permeate and retentate will be evaluated for heat transfer fouling tendencies. Modification of ERRC’s existing fuel ethanol processing model. Membrane processing steps will be added using the data generated. Upon completion of the work, knowledge gained from this research can be expected to lead to development of process strategies that will serve to avoid or reduce microbial contamination, remove antibiotics from coproducts, and mitigate evaporator fouling. With the new knowledge gained, processors potentially will have opportunity to separate microbial and antibiotic components prior to evaporator operation that, in turn, would allow opportunities to significantly improve process efficiency.
3. Progress Report:
In the production of fuel ethanol, all dry grind plants use evaporators to remove water from thin stillage. Thin stillage contains 90% water and a portion is concentrated in evaporators and mixed with wet grains to produce distillers dried grains with solubles (DDGS). Thin stillage forms deposits on evaporator surfaces and reduces efficiency by consuming more energy per unit of water evaporated. Fouling deposits increase over time and require periodic evaporator shutdown for cleaning. Costs associated with fouling include labor and equipment to clean fouled heat transfer surfaces, increased capital, cleaning chemicals, production losses and environmental impact from evaporator cleaning chemical disposal. Proteins, carbohydrates, fats and fiber may increase evaporator fouling rates; studying the causes of increased fouling of thin stillage is complicated by its perishable nature, variable composition and complex composition. Experimentation using membrane processing and thin stillage are ongoing. During the year, synthetic thin stillage was created using water, glucose and starch mixed at varying ratios and at varying total solids concentrations. The synthetic thin stillage was tested for fouling tendencies using an annular fouling probe. Higher concentrations of starch in synthetic thin stillage (relative to glucose concentrations) shortened time needed to reach maximum probe temperature. For total solids concentrations between 1 and 10%, fouling resistance (Rf) increased mainly because of the starch present in synthetic thin stillage, while glucose had a smaller effect on Rf. Synthetic thin stillage containing only glucose did not foul after 10 hr of testing. Additional work will investigate the interactions of protein and fat components with carbohydrates during fouling processes. A poster was presented showing the results at the Corn Utilization and Technology conference in Indianapolis, IN.